Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Nomeie as duplas mistas para o ano anterior a 1991 e as duplas masculinas de David Jepson e Buck Ryan.
 ###Tabelas: CREATE TABLE most_goals_in_a_la_liga_season_at_least_100_goals (most_goals_in_a_la_liga_season_at_least_100_goals_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Club VARCHAR, Season VARCHAR, Goals INT, Apps INT) CREATE TABLE expeditions (expeditions_id AUTO_INCREMENT PRIMARY KEY, Expedition VARCHAR, Crew VARCHAR, Launch date VARCHAR, Flight up VARCHAR, Landing date VARCHAR, Flight down VARCHAR, Duration (days) VARCHAR) CREATE TABLE 60_metres (60_metres_id AUTO_INCREMENT PRIMARY KEY, Lane INT, Name VARCHAR, Country VARCHAR, Mark VARCHAR, React INT, Points INT) CREATE TABLE newspapers (newspapers_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Frequency VARCHAR, Language VARCHAR, City VARCHAR, Website VARCHAR) CREATE TABLE winners (winners_id AUTO_INCREMENT PRIMARY KEY, Year INT, Men's singles VARCHAR, Women's singles VARCHAR, Men's doubles VARCHAR, Women's doubles VARCHAR, Mixed doubles VARCHAR)  
SELECT Mixed doubles FROM winners WHERE Year < 1991 AND Men's doubles = david jepson buck ryan